Modern diagnostic medicine depends on the routine testing of biological samples from sources such as blood, serum, spinal fluid, urine, tissue specimens, etc. In addition, many other industries and research facilities run both chemical and biological tests in large numbers. In order to perform the running of large numbers of tests efficiently, accurately, and safely, the "hardware" used in the performance of the tests can be of critical importance.
Microtiter plates or "microplates" were introduced in the 1960's to facilitate laboratory testing in situations where a large number of tests were run simultaneously. The most typical microplates contain ninety-six (96) molded plastic wells (in an 8.times.12 array) with a typical sample volume capacity of about 200 microliters. A wide variety of mechanical fluid handling devices are now available so that specimens, chemical solutions and other liquids can be transferred into the wells. Usually a row of eight (8) or twelve (12) wells are filled simultaneously, but some handling devices can simultaneously add sample to all of the wells.
The design of the microplate is less than optimal in several ways. First, the microplate wells are open wells. Most microplates have loose fitting lids, but these do not seal the top of the well. As a consequence, liquid can spill out of the well or aerosols can form during filling. This can ruin the test and may also create a hazard if the testing involves infectious material. Moreover, liquid can evaporate from the wells. This can also ruin the test or limit the duration of the test. Thus, it is preferable to have testing hardware which can be easily sealed.
Second, although filling devices are available to fill more than one well at a time, these devices are costly and still time consuming to use. It would, therefore, be preferable for the testing device to be easy and fast to fill without expensive equipment.
Third, the volume of the well is relatively large. Often the sample is in short supply or the testing reagents are costly. It would, therefore, be preferable to have wells with a smaller capacity.
Finally, microplates are relatively large and heavy. They take up a great deal of space in the laboratory refrigerators and incubators, and they are costly to ship in large quantities.
An improvement over the microplate format is disclosed in U.S. Pat. No. 4,038,151 to Fadler et al. This device has an enclosed format (minimizing spills and aerosols) and is relatively smaller and lighter in weight. The well volume is reduced and thus requires a smaller sample size.
Nonetheless, this design has distinct disadvantages as well. In order to fill the Fadler test device with liquid, the air in the wells must leave so that the liquid can enter. The Fadler et al. device accomplishes this with a very slow, elaborate, and expensive procedure in which the device is placed in a vacuum chamber and the air is removed as the vacuum is created. When the vacuum is released, the liquid flows into the device. Since, even with the elaborate vacuum system, the air removal may not be complete, this design provides a small well connected to each main well as an appendage for the purpose of holding residual air. These appendage wells, take up space that might otherwise be used to accommodate more test wells.
An alternative to this design is disclosed in U.S. Pat. No. 4,806,316 to Johnson et al. This device allows air to escape from the wells via escape channels which connect back to the air space in the reservoir from which the sample originates. This additional channelling is necessary so that the liquid can flow to the wells. Not only does this additional channelling take up space in the device making it larger or reducing the number of test wells that will fit on it, but, more importantly, this design requires the use of a reservoir with a special cap having two vent pipes, which is an expensive component when, for reasons of potential contamination, such reservoir and cap must be single-use and disposable.
What is needed is a device that is simpler, faster and more economical to fill. Such a device should not require the use of filling procedures having additional risk nor which require expensive and cumbersome equipment, but it should be able to accommodate the simultaneous filling of a large number of test wells.